This application claims the priority of German Application No. 196 24 041.7, the disclosure of which is expressly incorporated by reference herein.
In modern vehicles, a data-receiving write and read memory stores not only the parameters required for the vehicle variants and the country variants but also documentary data, such as the total mileage driven as well as service data. By means of special, high-expenditure methods, such as the redundant filing of the data also in other control units as well as by coding and a software write protection, these data are made as inaccessible as possible so that a manipulation of these data is made more difficult.
Although the required technical expenditures with respect to a manipulation of this type of memory have risen in comparison to changing the previously customary total mileage counter (referred to in the following as "GWSZ"). In a mechanical roller-type counter, the above-mentioned conventional measures have all not been able to prevent a manipulation of the content of GWSZ and of other documentary data.
There is therefore needed a process of the above-mentioned type which offers increased protection against a manipulation of the memory.
This need is met according to the present invention by a process for changing an electronic memory for use-related data of a vehicle. The changed new data and the old data maintained in the memory are sent to a comparator. The comparator will permit the taking-over of the new data into the memory only if the new data are changed with respect to the old data in a manner conforming with the use.
The comparator is now a part of a logic unit which compares the new and the old data with one another and will permit an overwriting of the memory with the new data only if the difference of the two satisfies defined plausibility criteria.
If the documentary data are, for example, the overall operating time of the vehicle, the new data can be taken over only if they correspond to a fairly long total operating time. However, not only the type, e.g. in this case, the increase of the total operating time, but also the extent by which the data are changed falls into the scope of the present invention. The change must be plausible. This prevents making an accidental change of data which does not correspond to the actual conditions. For example, an unintentional doubling of the total operating time can be excluded in this manner.
In the case of the GWSZ (total mileage counter), the invention is represented as follows.
The new data are taken over and used for overwriting the old data only if the new data correspond to an increased running performance of the vehicle and if they differ from the old data by a predetermined value. This value can be used as the upper limit and correspond, for example, to a change of the running distance by two kilometers.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.